A recent study by the U.S. Geological Survey (USGS) under the National Water-Quality Assessment (NAWQA) program characterized the ground-water quality in a part of the Denver, Colorado, metropolitan area. The study provides an assessment of water-quality conditions in an alluvial aquifer that drains into the South Platte River. Thirty wells randomly distributed in residential, commercial, and industrial land-use settings were sampled once in 1993 for a broad range of compounds. Nutrients, pesticides, and volatile organic compounds (VOC's), all of which are generally associated with human activities, frequently were detected in the urban wells sampled. Nutrients and VOC's occasionally exceeded drinking-water standards.